Definition
Polymerseparationmembrane:asemi-permeablemembranewithselectivepermeationfunctionmadeofpolymermaterials.Usingsuchasemi-permeablemembrane,usingpressuredifference,temperaturegradient,concentrationgradientorpotentialdifferenceasthedrivingforce,thegasmixture,liquidmixtureororganicandinorganicsolutionsareseparated,whichhasthecharacteristicsofenergysaving,highefficiencyandcleanliness.
Polymerfunctionalmembrane:amembranematerialwithselectivepermeability,andalsoapolymermaterialwithspecialmasstransferfunction,usuallycalledseparationmembrane,alsocalledfunctionalmembrane.Membraneseparationofsubstancesgenerallydoesnotundergophasechangeanddoesnotconsumephasechangeenergy.Atthesametime,ithasgoodselectivity.Themembranedividestheproductonbothsidesandiseasytocollect.Itisaseparationmaterialwithlowenergyconsumptionandhighefficiency.Fromafunctionalpointofview,thepolymerseparationmembranehasthefunctionsofmaterialseparation,materialidentification,energyconversionandmaterialconversion.
Includingmicrofiltrationmembranes,ultrafiltrationmembranes,polymerseparationmembranes,reverseosmosismembranesandnanofiltrationmembranes.
Classification
Accordingtothefunctionofuse,itcanbedividedinto:mixtureseparationmembrane,drugreleasesustained-releasemembrane,andseparationprotectivemembrane;
dividedaccordingtothenatureoftheseparatedsubstance:Gasseparationmembranes,liquidseparationmembranes,solidseparationmembranes,ionseparationmembranesandmicrobialseparationmembranes;
Accordingtotheparticlesizeoftheseparatedmaterial,itisdividedinto:ultra-finefiltrationmembrane,ultra-filtrationmembraneandmicro-filtrationmembrane;
Accordingtothefilmformationprocess,itisdividedinto:depositionfilm,solventinjectionfilm,interfacefilmanddynamicfilmformation;
Accordingtothefilmproperties,itisdividedinto:densityfilm,phasechangefilmformation,emulsificationMembraneandporousmembrane.
Materialtypesandapplications
1.Cellulose(CA\CN\CN-CA)
Materialcharacteristics:widesources;easytoprepare;filmformationGood;strongchlorineresistance;smoothsurface;noteasytoscale;pollutionresistance,lowproteinadsorption.ButthePHvalueisnarrow,PH=3-7,lowtemperature,poorchemicalresistance,easytohydrolyze,andpoorcompaction,Poorantibacterialproperties.
Typicalapplications:sterilizationandfiltrationoflargeandsmallinfusions;sterilizationandfiltrationofinjections;sterilizationandfiltrationofvaccines,biologicalproductsandantibiotics;cellculturemedia,diagnosticreagentsandcontainingproteinsandvitaminsSterilizationandfiltrationofpreparationswithpreservatives;Sterilizationandfiltrationofgeneticengineeringproducts;Sterilizationandfiltrationofeyedrops;Sterilizationandfiltrationofserumandplasmaseparation.
Otherapplications:Foraqueoussolutions(CA);pretreatment,particledetectionorparticleremoval(CN\CN-CA),largeporemembrane(8um\5um\3um)isespeciallysuitableforcellcollection,biotaxisanalysis,smallporemembrane(suchas0.45um)issuitableForparticlecollection,asmallerporemembrane(0.22um\0.1um)issuitableforsterilizationorremovalofmycoplasma.Dedicatedtorapiddiagnosisandtransfertechnology(CN)
Sterilizationmethods:autoclaving,ethyleneoxidefumigationorﻻ-raysterilization.
2.Regeneratedcellulose(RC)
Materialcharacteristics:RCisalsoknownascelluloseⅡ.Itisusuallyobtainedbydissolvingnaturalcellulosethroughchemicalmethodsandthenprecipitation.ItsmolecularweightItisgenerallylowerthannaturalcelluloseandhaslowercrystallinity.Ithasgoodhydrophilicity,strongpollutionresistance,lowfluxattenuation,goodsolventresistance,andcanwithstandmostorganicsolvents.Alcoholresistance\Ketoneresistance\saturatedhydrocarbonresistance\aromatichydrocarbonresistance\chlorinatedhydrocarbonresistance\lipidsandproticpolarsolvents(suchasdimethylformamide,etc.).Ithasnotoxicsideeffectstoorganismsandhasgoodbiocompatibility.Lownon-specificadsorptioncapacity.Resistance.
Typicalapplication:Themainpurposeisorganicsolventparticleremovalfiltration.Speciallyusedforclarificationorsterilizationfiltrationofnon-aqueoussolutions.
Sterilizationmethods:autoclaving,dryheatsterilization(180degrees),ethyleneoxidefumigationorγ-ray
3.Polyamide(nylon-6,nylon-66)
Materialcharacteristics:mainlycomposedofdibasicacidandDiamineoraminoacidlactamisobtainedbypolycondensationorself-polymerization.Becauseoftheamidegroup,itiseasytoformhydrogenbonds,hasstrongmechanicalstrengthandgoodhydrophilicity.Comparedwithnylon-6,nylon-66hashighermechanicalstrength,highertemperatureresistance,andbetterlowtemperatureresistance.Bothhavegoodalkaliresistance,goodresistancetoorganicsolvents,greaseresistanceandoilresistance(mineraloilandvegetableoil)butnotacidresistance.Highproteinabsorption.
Typicalapplications:sterilizationandfiltrationofantibiotics,vitaminsandotherfermentedproducts;sterilizationandfiltrationofchemicalindustryproducts;sterilizationandfiltrationofveterinarymedicines;sterilizationandfiltrationoforalliquidsandeyedrops;pharmaceuticalindustrySterilizationandfiltrationofinfusionandinjections;Sterilizationandfiltrationofphysiologicalsalineandothersolvents;Sterilizationandfiltrationofotherlow-costproductsinthepharmaceutical,chemicalandcosmeticindustries.
Otherapplications:Nylonmaterialsareparticularlysuitableforfilteringalkalinesolutions;usedforparticleremovalandfiltrationoforganicsolvents.Transferfilm.DNAandRNAattachment;southern\northerntransfer;geneprobedetection;nucleicaciddotblot;DNAfingerprinting;colonytransfer.However,duetotherelativelyhighadsorptionofnylonmembranes,itisgenerallynotrecommendedforsterilizationfiltrationofculturemediaorfiltrationofbiologicalsamplessuchasproteinliquids.
Sterilizationmethod:autoclaving,ethyleneoxidefumigation.
4.Polysulfone(PS)\polyethersulfone(PES)
Materialcharacteristics:BisphenolApolysulfoneisthemostcommonlyusedmembranematerial.Doublecalledpolyphenyleneethersulfone.Inordertoimprovethehydrophilicityofthematerial,itisoftensulfonated.Bothhaveexcellentresistancetochemicalsolvents.Inadditiontostrongpolarsolvents,concentratedsulfuricacidandconcentratednitricacid,itisresistanttogeneralacids,Alkali,salt,alcohol,aliphatichydrocarbonandotherchemicalreagentsarestable.Ithasgoodsteamresistanceandcanwithstandthelong-termerosionof50mg/Lfreechlorine.ButtheUVresistanceispoor.Theyareallsolubleinchlorinatedhydrocarbons,swelledinketonesandesters,andpartiallydissolved.
Typicalapplications:sterilizationandfiltrationoflargeinfusionsolutions;sterilizationandfiltrationofbuffersolutions;sterilizationandfiltrationofwaterforinjection;sterilizationandfiltrationofcleaningsolutionsanddisinfectants;sterilizationandfiltrationofbulkliquidmedicines;Anyliquidthatrequiresultra-highflowrateisfiltered.
Sterilizationmethod:autoclavingorethyleneoxidefumigation.
5.Polyvinylidenefluoride(PVDF)
Materialcharacteristics:PVDFisacrystallinepolymer.Ithasexcellentweatherresistanceandchemicalstability.Itisnotcorrodedbyacids,alkalis,strongoxidantsandhalogensatroomtemperature,andisstabletoorganicsolventssuchasaliphatichydrocarbons,aromatichydrocarbons,alcohols,andaldehydes.Fumingsulfuricacid,strongbases,ketones,andetherscanswellorpartiallydissolvethem.
Typicalapplications:hydrophobicPVDFinsteamfiltration;sterilizationandfiltrationofvariouscorrosivegases;sterilizationandfiltrationoforganicsolvents;sterilizationandfiltrationofcompressedairinthepharmaceuticalindustry;Sterilizationfiltrationandotheraspects.HydrophilicPVDFiswidelyusedinsterilizationfiltrationinbiopharmaceuticalsduetoitslowproteinadsorptioncapacity.PositivelychargedPVDFcanbeusedtoremoveendotoxins.
Otherapplications:transfermembrane,DNAandRNAattachment;southern\northerntransfer;geneprobedetection;nucleicaciddotblot;DNAfingerprinting;colonytransfer.
6.Polytetrafluoroethylene(PTFE)
Materialcharacteristics:PTFEisalinearthermoplasticpolymerfromthepointofviewofitsmolecularstructure.Ithasexcellentchemicalstabilityandexcellentweatherresistance.Inadditiontometalsodium,fluorineanditscompoundshaveacertaincorrosiveeffectonit,itcanwithstandanyotherstrongacids,strongalkalis,greasesandorganicsolvents.Naturallystronghydrophobicity.
Typicalapplications:Becauseofitsnaturalstronghydrophobicity,itiswidelyusedinthefieldofbiopharmaceuticalsforairsterilizationandsterilization,suchasthesterilizationandfiltrationoftheintakeandexhaustgasoffermentationtanksandthesterilizationandfiltrationofstoragetanks..Stronglycorrosivesolventsterilizationfiltrationandorganicsolventsterilizationfiltration.HighsurfacetensionsolventsmustbehydrophilizedtomodifyPTFE.
7.Polypropylene(PP)
Materialcharacteristics:duetothedifferenceinthespatialarrangementofmolecularchains,itisdividedintoisotacticandatacticpolypropylene.Thematerialofthemembraneisisotacticpolypropylene.Isotacticpolypropyleneisahighlycrystallinethermoplasticresin.Ithasgoodheatresistanceandexcellentchemicalstability.Atroomtemperature,itcanwithstandmostchemicalsolventsexceptstrongoxidants.
Typicalapplication(thermalsprayfiberflatfilm):appliedtoimpuritiesorparticlesinliquidorgas.Notasasterilizationfilter.Pre-filtrationofinjections;particlefiltrationofdeionizedwatersystem;particle-removingfiltrationofchemicalsolvents;particle-removingfiltrationofbiologicalproducts.Clarificationandfiltrationofvarioussolventsorsolutions.
Sterilizationmethod:autoclaving,ethyleneoxidefumigation.
Performance
Permeability
Thepermeabilityofthemembraneisoneoftheveryimportantpropertiesofpolymermembranematerials.AlmostallreportsonthemembraneinvolveThisperformance.
Theexperimentalresultsshowthatthepermeabilityofthemembraneiscloselyrelatedtotemperature,membranethickness,chemicalcomposition,preparationprocessconditionsandthemicrostructureofthemembrane.Theoxygenandnitrogenpermeabilityofmethylsiliconerubber,ethylene-propylenerubber,low-densitypolyethyleneandnaturalrubbermembraneshavebeenstudied.Itisfoundthatthedependenceofthemembrane'spermeabilityontemperatureisonlyrelatedtothematerialofthemembrane.Thegaspermeabilityofpoly-4-methyl-1-pentene(PMP)membranesincreaseswithtemperatureatdifferenttemperatures.
Theinfluenceofthechemicalcompositionofthemembraneonpermeabilityisbothauniversalandunderstandablephenomenon.TransmittanceandwaterpermeabilityarebetterthancopperpowderfilmandPVAfilm,andtherupturestrengthisclosetothatofPVAfilm.Theoxygenandnitrogenseparationcoefficientofpolydimethylsiloxane(PDMs)isabout2.0lowerthanthatofpolyvinylalcoholmembrane,andthestrengthofthemembraneisalsopoor.
Theinfluenceoffilmformingprocessconditionsonfilmperformance.TheresultsofthediscussionontheevaporationprocessofthecastingliquidofthepolyvinylchlorideultrafiltrationmembraneprovethattheevaporationtimeisthemainfactoraffectingtheperformanceofthePVCultrafiltrationmembrane.Withtheextensionoftheevaporationtime,thegeneraltrendistocausethewaterfluxofthemembranetoincrease,whiletherejectionratedecreases.Asthethicknessofthefilmincreases,thewaterfluxofthefilmdecreases.ThetemperatureofthegelmediumalsohasaneffectontheperformanceofthePVCultrafiltrationmembrane.
Distillability
Membranedistillationisamembraneseparationprocesspoweredbyvaporpressuredifference,whichischaracterizedbytheabilitytoprocesshigh-concentrationsolutionsundernormalpressureandappropriatetemperature.Forexample,intheprocessofmembranedistillationofaqueoussolutions,thehydrophobicmicroporousmembraneseparatestheaqueoussolutionsatdifferenttemperatures,whilethewatervaporonthewarmsidecontinuouslyentersthecoldsidethroughthemembraneporesandcondensesundertheactionofthevaporpressuredifference,therebyreachingthemembranePurposeofdistillation.Forexample,whentheporesizeofthepolyvinylidenefluoridemembraneis0.1um,thetemperaturedifferenceis30℃(warmside50℃,coldside20℃),thebrineconcentrationis0.3mol,thebrineflowrateis10ml/s,andthedistillationfluxis55to65kg/m2·D,theinterceptionrateiscloseto10%.
Electricalproperties
Mostpolymersarenon-conductivematerials,sotheycanbeusedasinsulatingmaterialsintheelectricalindustry.Withthedevelopmentofmembranematerialsresearch,membraneswithvariousgoodelectricalpropertieshavealsoappearedoneafteranother.Forexample,Polypyrrole(PPY)isamaterialwithhighconductivity,butitspracticalityisgreatlyrestrictedduetoitsinsoluble,infusible,anddifficulttoprocessshortcomings.Alotofresearchworkistoobtainpolymercompositeswithhighmechanicalpropertiesandconductivefunctionsbycompoundingpolypyrrolewithotherflexiblepolymersatthemolecularlevel.
Preparationmethod
1.Inducedfilmformation
Acrylphthalamide(AM)canbemadeintoacrystallinepolyacrylamidefilmbyinducedfilm-formingpolymerization.CoatthemixedtransparentaqueoussolutionofAMgelatinandphotosensitizerontheglasssurface.Duetotheinductionofgelatinmolecules,AMmolecules,watermoleculesortheirassociatedmoleculesareevenlydistributedontheglasssurface.AMformsafilmatroomtemperature.Crystallization,sphericalcrystalswithadiameterofseveralcentimeterscanbeobtained.Afterbeingirradiatedwithultravioletlightandpolymerized,thesmallwaferslosetheirobviousedgesandcornersandbecomegranular.WhenobservingthePAMspherulitesthatinducedfilm-formingpolymerizationwithanorthogonalpolarizingmicroscope,itwasfoundthatithadanopticallyanisotropiceffect.Themembraneistreatedwithboilingwatertoobtainalargespherulitefilmmaterialwithacertainstrengthandarelativelyuniformporedistribution.Itisanidealopticalfilm.
2.Filmformationbycompleteevaporation
Useamixtureofdimethylformamide(DMF)andtetrahydrofuran(THF)asthesolvent,ethyleneglycolastheporogen,andpolyurethane(PU)Isthesubstrate,andthePUporousfilmcanbepreparedbythecompleteevaporationmethod.Theexperimentalresultsshowthatthestructureandperformanceofthemembranearecloselyrelatedtotheevaporationrateconstant.Forexample,changingthecompositionofthecastingliquidandthefilm-makingprocessconditionscanproduceavarietyofporousmembraneswithdifferentrequirements.TheclinicaltestresultsprovethatthismembraneisagoodskinsubstituteMaterial.
3.Surfacemodificationbyplasmapolymerization
BlendsystemofpolyvinylchlorideandliquidcrystalN-ethoxybenzylidene-butylaniline(EBBA)(70/30)Ithasgoodcompatibilityandcangreatlyincreasetheairpermeabilityofthefilm,butthereisaproblemofliquidcrystallossduetovolatilization.Theuseoffluorocarbonshasgoodanaerobicperformance,andthesurfacemodificationofthecumulativecompositemembranebyplasmapolymerizationcanincreaseitsoxygenandnitrogenseparationcoefficient.Theexperimentalresultsshowthatthedepositionthicknessofthefluorocarbonpolymeronthefilmsurfacemainlydependsonthedepositiontime,anditscrosslinkingdegreeincreaseswiththeincreaseoftheinputenergyvalueofthemonomerflowrate.WhenthemonomerflowrateissmallandtheprecipitationtimeisshortUndertheseconditions,amodifiedcumulativecompositemembranewithahigherαvaluecanbeobtained.
4.Film-formingsubstancefunctionalizationmethod
Thefilm-formingsubstancefunctionalizationmethodismainlytoconnectthefunctionalsubstancetothefilm-formingsubstancethroughachemicalreaction,andthentocastorThephaseinversionmethoddirectlyformsafilm,whichisacommonmethodforpreparingintegratedsmartfilms.ApH-responsivesmartmembraneofpolyvinylalcohol/polyacrylicacidwithaninterpenetratingnetworkstructurewaspreparedbyblendingandcross-linking.Themembranehasdifferentselectivepermeabilitypropertiesforurea,guaiacolglyceride,L-tryptophan,andVB12..
5.Surfacegraftingmethod
Surfacegraftingmethodisfirstthroughchemical(radicalinitiator,ozone,etc.)orphysicalmeans(suchasultravioletlight,plasma,high-energyradiation(Photo,etc.)Generatereactivecentersonthesurfaceofexistingcommercialpolymerfilms,andthenusetheseactivecenterstoinitiatepolymerizationofothermonomersonthesurfaceofthefilm,therebygenerating"polymerbrushes."Thesmartfilmpreparedbythegraftingmethodisshowninthefigure.Thegraftingmethodcanbedividedintochemicalgraftingmethod,plasmagraftingmethod,lightgraftingmethodandhigh-energyradiationgraftingmethodaccordingtothedifferentfreeradicalgenerationmethods.
6.Blendingmethod
Blendmodificationisanewmethodforpreparingsmartfilms.Theblendingmethodhasgreatadvantagesduetothecombinationofthepropertiesofvariousblendedmaterials.Theproblemthatshouldbepaidattentiontoinblendingisthecompatibilitybetweentheblendedmaterials.Itsadvantagesare:modificationandfilmformationarecarriedoutsimultaneously,theprocessissimple,nocumbersomepost-processingstepsarerequired,andtheindustrializationofmaterialsisextremelyeasytorealize;Theagentcancoverthesurfaceofthemembraneandtheinnerwallofthemembraneporesatthesametimewithoutcausingdamagetothemembranestructure.Theblendingmethodhasmadegreatprogressinthepreparationofhydrophilicporousmembranes,butthedevelopmentofsmartmembraneshasjustbegun.
Application
Highmolecularpolymermembranesarewidelyusedinvariousmembraneseparationprocesses.Theperformanceofmembranematerialsdirectlydeterminestheperformanceofthemembraneseparationprocess.Therefore,thedevelopmentofmembraneswithhighselectivity,highflux,basicallydefect-freeandlarge-scaleproductionhasalwaysbeenthefocusofmembraneseparationtechnologyresearch.
Membranedistillationtechnologyhasbeenextensivelystudiedinthefieldsofseawaterandbrackishwaterdesalination,wastewatertreatment,low-temperaturefruitjuiceconcentration,andtraditionalChinesemedicinepreparation.Becausemembranedistillationdesalinationtechnologycanutilizelow-gradeenergy(suchaswasteheat),Solarenergy,etc.)asitsdrivingforce,soitisgettingmoreandmoreattentionintoday'senergyshortageandwatershortage.However,lowdistillationfluxandexpensivemembranematerialshavebecomethekeytorestrictingthecommercialapplicationofmembranedistillationtechnology.
Therearethreemaintypesofpolymermembranematerialsused,namelypolytetrafluoroethylene(PTFE),polyvinylidenefluoride(PVDF)andpolypropylene(PP).Theyhavegoodhydrophobicproperties,andthePTFEmembranehasthebesthydrophobicity.Intermsofoxidationresistanceandchemicalstability,PTFEmembraneissuperiortotheothertwomembranes,whichmakesPTFEmembranemorewidelyusedinmembranedistillationprocess;PVDFmembraneisthesecondbest;PPmembranehasrelativelypoorchemicalstabilityandoxidationresistance.Butbecauseofthelowprice,themarketiswidelyused.